Plating technology is employed, for example, to deposit a metal in fine interconnect trenches or holes, or resist openings formed in a surface of a wafer, or to form bumps (protruding electrodes), which are to be electrically connected to package electrodes or the like, on a surface of a substrate. Plating technology is also employed to fill a metal into via holes in the production of an interposer or a spacer which has a large number of via plugs vertically penetrating therethrough and which is to be used in so-called three-dimensional packaging of semiconductor chips.
For example, it is common practice in TAB (Tape Automated Bonding) or flip chip to form protruding connection electrodes (bumps) of gold, copper, solder or nickel, or of multiple layers of such metals at predetermined portions (electrodes) of the surface of a semiconductor chip, having interconnects formed therein, so that the semiconductor chip can be electrically connected via the bumps to package electrodes or TAB electrodes.
Electroplating of a wafer is performed by applying a voltage between an anode and the wafer, which serves as a cathode, while keeping them immersed in a plating solution. In order to enable the plating solution to easily enter recesses or through-holes formed in the wafer surface, the wafer is subjected to a pre-wetting treatment which is to replace air, existing in the recesses or through-holes, with a pre-wetting liquid. The pre-wetting treatment is performed by immersing the wafer in the pre-wetting liquid held in a pre-wetting tank (see, for example, Japanese Patent No. 4664320).
However, in the above-described conventional pre-wetting treatment, the entire wafer is immersed in the pre-wetting liquid. Therefore, it is necessary to use a large amount of pre-wetting liquid. In addition, it takes considerable time to fill the pre-wetting liquid into the pre-wetting tank, and to discharge the pre-wetting liquid from the pre-wetting tank.
In order to solve such problems, a spray-type pre-wetting treatment has been proposed which involves spraying a pre-wetting liquid onto a wafer surface. However, the pre-wetting liquid with a high pressure can cause collapse of patterns formed on the water. With such a background, there is a demand for a soft pre-wetting technique which does not cause pattern collapse.